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Nitrogen metabolism by lactating ewes and their lambs
G P Lynch1, T H Elsasser, T S Rumsey
1Ruminant Nutr. Lab., U.S. Department of Agriculture, Beltsville, MD 20705.
Journal of Animal Science
|December 1, 1988
Summary
Ewes fed moderate protein diets produced better nitrogen balance. Ewes nursing twin lambs had lower nitrogen retention and altered metabolic profiles, indicating increased nutritional demands.
Area of Science:
- Animal Nutrition
- Ruminant Physiology
- Reproductive Biology
Background:
- Maternal nutrition significantly impacts lactation and offspring development.
- Understanding nutrient partitioning in lactating ewes is crucial for optimizing production.
- The interplay between diet protein and litter size affects maternal metabolic status.
Purpose of the Study:
- To investigate the effects of dietary crude protein (CP) levels and litter size on nitrogen (N) balance and metabolic indicators in lactating ewes.
- To determine how moderate protein (MP) versus low protein (LP) diets and single (S) versus twin (T) lamb nursing influence maternal N utilization and key blood metabolites.
- To assess the impact of these factors on hormonal profiles and nutrient allocation for milk production.
Main Methods:
- A 2x2 factorial experiment with 20 multiparous ewes and their lambs.
- Ewes were fed either MP (15% CP) or LP (10% CP) diets ad libitum.
- Nitrogen balance trials were conducted at weeks 2, 4, and 8 of lactation, alongside measurements of serum metabolites and hormones.
Main Results:
- Moderate protein diets improved nitrogen balance, digestion, and retention compared to low protein diets.
- Ewes nursing twin lambs exhibited lower nitrogen retention and altered serum urea-N, beta-hydroxybutyrate, glucose, and amino acid profiles.
- Hormonal changes included increased insulin, higher triiodothyronine (T3) and thyroxine (T4) in ewes nursing twins, and a lower T4:T3 ratio with LP diets.
- Ewes on LP diets nursing twins utilized retained nitrogen and body reserves for milk production by week 2.
Conclusions:
- Dietary protein content and litter size significantly influence nitrogen utilization and metabolic status in lactating ewes.
- Low protein diets combined with nursing twin lambs impose substantial metabolic stress, leading to the mobilization of body reserves for milk synthesis.
- Optimal maternal nutrition is essential to meet the demands of twin lambs and maintain ewe body condition throughout lactation.